Polyesters are widely used as extrusion and injection molding resins for application such as fibers, films, sheeting, automotive parts, and food and beverage containers. In manufacturing polyesters, handling issues arise with respect to supplying these monomers to the reactor since glycols and dicarboxylic acids are many times solid at ambient conditions.
Conventional monomer feeds to polyester processes are slurries, melts or direct solid feeds.
Isosorbide is generally known in the art as a monomer for incorporation into certain types of polyesters. Isosorbide is a diol that can act as a partial substitute for other diols including ethylene glycol and 1,4-cyclohexanedimethanol. It may be incorporated as a monomer into polyesters that include terephthaloyl moieties. Isosorbide improves the thermal properties of certain polyesters by giving the polymer a higher glass transition temperature. This monomer may also enhance the polymer's performance in a variety of applications where conventional polyesters cannot perform the same functions. These properties provide value to markets such as PET rigid containers and thermoplastics as well as others.
Copolymers containing isosorbide moieties, ethylene glycol moieties, and terephthaloyl moieties have been previously disclosed but in limited instances. A copolymer containing these three moieties, in which the mole ratio of ethylene glycol to isosorbide was about 90:10, was reported in the published German Patent Application No. 1,263,981 (1968). The polymer was used as a minor component (about 10%) of a blend with polypropylene to improve the dyeability of polypropylene fiber. It was made by melt polymerization of dimethyl terephthalate, ethylene glycol, and isosorbide, but the process conditions were described only in general terms in the publication.
U.S. Pat. No. 6,063,464 describes a polymerization process for isosorbide containing polyesters where the diols (including isosorbide) are mixed with the dimethyl ester of the diacid in the presence of an ester interchange catalyst which causes exchange of the diol for the methyl group of the dimethyl esters through a transesterification reaction. The catalyst may be included initially with the reactants and/or may be added one or more times to the mixture as it is heated. This patent also teaches that some of the monomers may need to be included in excess at the beginning of the polymerization reaction and removed by distillation as the reaction proceeds.
Published PCT Application WO 99/54119 describes a polyester polymer and method for making the polyester, wherein the polyester is prepared by (1) combining in a reactor a monomer containing a diacid moiety; a monomer comprising a diol moiety; and a monomer containing an isosorbide moiety; with a condensation catalyst suitable for condensing aromatic diacids and diols; and (2) heating the monomers and catalyst to polymerize the monomers to yield a polyester having an inherent viscosity of at least about 0.15 dL/g. This publication describes the mixing of monomers comprising the polyester (including isosorbide) in the beginning of the process.
The market for isosorbide containing polyesters requires good resin quality which is dependent on the product of high purity material and resin that is prepared by an efficient, economical, continuous process. With respect to the efficient, economical process, it is important to provide a process, which integrates readily into conventional melt phase polyester manufacturing equipment. This requires a practical way of conveying and storing the isosorbide monomer from its manufacturing location to the polyester process where it is used.